Post-consumer or post-industrial glass is currently largely disposed of in landfills because it is of mixed color, is mixed with odorous non-glass residue, and because there is at present no satisfactory system for producing clean glass particles from the typical waste stream.
Clean glass particles that have rounded edges, are free of odor and have very low levels of organics could be used as a substitute for crystalline silica sand or crushed stone in a variety of applications and uses. These uses include but are not limited to: making glass containers, fiberglass or specialty glass; abrasives for blasting, scouring cleansers, sawing and sanding; filtration for swimming pools or other water filtration; manufacturing bricks, tiles or countertops; recreational uses on golf courses, tennis courts, beaches, and playgrounds; roofing materials; as a substitute for natural sand or crushed stone in manufacturing concrete products; and for general construction and landscaping uses.
For glass particles to be suitable for many of the uses listed above, the organic concentration must be less than 0.5%, as measured by a standard Loss-On-Ignition (LOI) test. As is well known to those of skill in the art, LOI refers to the mass loss of a combustion residue whenever it is heated in an air or oxygen atmosphere to high temperatures. In the cement industry, use of the term LOI normally refers to a mass loss in a sample heated to 950° C. To combustion engineers, the term LOI normally refers to mass losses in samples heated to temperatures less than 950° C. These test methods establish a procedure for determining LOI values for combustion residues heated to 750° C. or 950° C. LOI values from these test methods can be used by industries that utilize combustion residues in various processes and products.
The present inventor and others have disclosed in U.S. Pat. No. 7,413,602 a process and equipment for producing a fine glass powder that is useful as a pozzolanic constituent of concrete from post-consumer waste streams containing a large fraction of glass mixed with other materials. The present invention is directed primarily toward production of larger glass particles, e.g., of the size of grains of sand, and thus useful as a substitute for, e.g., sand in children's sandboxes. To be acceptable for such use the glass particles must have low levels of organics, as above, so as not to give off unpleasant odors, and of course all of the non-glass constituents of the waste stream must be completely removed.
One problem that has not previously been solved in the production of clean glass particles from a post-consumer waste stream is the removal of all paper from the glass particles. Large scraps of paper are readily removed, but tiny fibrous shreds are difficult to remove. Other processes and equipment that have been used in the industry to dry and process waste glass have used a rotary dryer or similar device with an open flame to burn off any residual paper. This process results in residual ashes mixed with the fine glass. As the glass is screened for size separation, it is found that the finer the particle size and grade of glass, the darker the color of the glass mix. The dark color can be attributed to the ash content in the glass.
The present inventor and others have disclosed in U.S. Pat. No. 7,413,602 a process for producing fine glass powder that includes the step of washing the glass particles in a water immersion system to remove paper and other contaminants. The present invention does not use water for washing the glass particles, and thereby eliminates the sediment-removal and water filtration steps that were required in that process.